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Long justifications are better placed on the side.
– egregApr 23 '14 at 8:40

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I agree with @egreg writing on top of relations etc is considered bad style in writing, and should be reformulated instead. Some of this may be fine on a blackboard, but not in print. Also remember \intertext{...} and its cousin \shortintertext{...} from mathtools
– daleifApr 23 '14 at 8:48

Thanks, I'll try to figure it out differently, maybe discuss it with professor for whom I write it. But sometimes it is something like from def 3.11(ii) in my language "only" z def 3.11(ii), so I might stick to it form time to time. But I guess "long justification" can stand for two and more characters sometimes.
– quapkaApr 23 '14 at 9:06

I had started with makebox but I was getting lots of errors so I gave up :-( I now see it was simple: I was missing the $ inside the makebox. I like this solution myself. I am going to upvote it!
– FionaSmithApr 23 '14 at 10:06

@FionaSmith -- I was thinking of array, but your OP mentioned that and that forced me to think what else ...
– JesseApr 23 '14 at 10:36

How to create a box with the same width of an other box? Instead of hardcoding the 3cm I'd like to do something like: \makebox[\getWidthOf{\overset{\text{some long text}}\leq}][x]{$\overset{\text{some text}}\leq$} to have the symbol with the shorter text take exactly the same space as the symbol with the longer text (and nothing more).
– BakuriuMay 4 '14 at 15:35

@Bakuriu -- Please check here tex.stackexchange.com/q/18576/34618. If this does not help, then you need to ask a new question since this is closed, not available of posting any.
– JesseMay 4 '14 at 16:30

Well although this would done the job It does not seem like a good solution for almost "two times a page" use. Still thanks, but I'll probably go with @egreg advice. But I might use it in some cases.
– quapkaApr 23 '14 at 9:02

Since this is math, an array would be better, with \begin{array}{@{}r@{}>{{}}c<{{}}@{}l@{}} (requires also the array package).
– egregApr 23 '14 at 9:04

@egreg I have added an example. I've not used array before and in the example I was looking at I was very confused by the whole string of @{}r@{} etc and didn't want to spend time looking it up! Since you provided the correct code, I've updated my example above.
– FionaSmithApr 23 '14 at 9:11

With @{} we remove the intercolumn space; the >{{}}c<{{}} construction adds empty atoms around the relation symbols in the c column so the spacing will be correct.
– egregApr 23 '14 at 9:13